The invention relates to a composite, comprising a Cu—Sn bronze matrix and filaments surrounded by the bronze matrix, wherein the filaments contain niobium (═Nb) or a Nb alloy. The invention further relates to a method for producing a superconductive element. The invention moreover relates to a superconductive element, in particular a multifilament wire, produced by the bronze route based on the bronze diffusion process, comprising filaments containing Nb3Sn.
Such composites, superconductive elements and methods for the production thereof are e.g. described in V. Abächerli et al., ASC 2004, Jacksonville (Fla.), Paper 4MR04, where the bronze route to Nb3Sn is described.
Nb3Sn is one of the few commercially relevant superconducting materials. It is used in particular for the production of high field magnetic coil systems.
There are basically three ways to produce Nb3Sn: the powder in tube (=PIT) process, the internal tin diffusion (=ISD) method, and the bronze route. The bronze route is of particular relevance in the production of magnetic coil systems.
The basic idea of the bronze route is to introduce Nb containing filaments into a Cu—Sn bronze matrix. Several (re-)bundling and elongating steps are usually applied. During a final annealing of this composite at typically 600-730° C., Sn from the bronze matrix diffuses into the Nb containing filaments and forms Nb3Sn. The Nb containing filaments are mostly dissolved.
Compared to Nb3Sn material made by PIT or ISD, Nb3Sn wires made by the bronze route have relatively low critical current densities jc at given temperature values (of about 4 K) and magnetic field strengths (of about 15 T) relevant for superconducting magnetic coil systems. This means that the maximum magnetic field strength obtainable with bronze route wires is relatively low.
It is therefore the object of the invention to provide a composite from which a superconductive element which has an improved, i.e. higher critical current density jc can be produced by the bronze route. Moreover, it is the object of the invention to provide a corresponding method of production for such a superconductive element, and to provide such a superconductive element itself.